METHOD AND DEVICE FOR THE GALVANIC APPLICATION OF A SURFACE COATING

Abstract

A method for galvanic application of a surface coating, in particular a chromium coating, to a body, for example a machine component. Before the galvanic application of the surface coating, a layer of a compound that can be oxidized by an electrolyte solution that is used, preferably a polyhydroxy compound with a viscosity of at least 1000 mPas at 25 C., is applied to the body. A method for galvanic application of a surface coating, in particular a chromium coating, to a body, for example a machine component, wherein the surface coating is carried out in a closed reactor in an at least two-stage, preferably three-stage process, is also disclosed. An electrolyte solution contained in the reactor at a temperature T1 for carrying out a subsequent process stage is substituted by an electrolyte solution at a temperature T2T1. A device for carrying out this method is also disclosed.

Claims

1-15. (canceled)

16. A process for electrochemical application of a surface coating to a body, the process comprising: applying a layer of a compound, which can be oxidized by an applied electrolyte solution and which has a viscosity of at least 1000 mPas at 25 C., to the body before the electrochemical application of the surface coating.

17. The process as claimed in claim 16, further comprising using a polyhydroxy compound as the compound to be applied to the body before the electrochemical application of the surface coating.

18. The process as claimed in claim 17, further comprising selecting the polyhydroxy compound from the group consisting of glycerol, carbohydrates and polyethylene glycol.

19. The process as claimed in claim 17, further comprising cleaning the body with an alcohol before application of the layer of the polyhydroxy compound.

20. A process for electrochemical application of a surface coating to a body, the processing comprising: carrying out the surface coating in a reactor in an at least two-stage process, wherein an electrolyte solution having a temperature T1 present in the reactor (2) is replaced by an electrolyte solution having a temperature T2T1 for carrying out a subsequent process step.

21. The process as claimed in claim 20, further comprising carrying out the replacement of the electrolyte solution having a temperature T1 by an electrolyte solution having a temperature T2T1 by introduction of the electrolyte solution having a temperature T2T1 into the reactor and resulting displacement of the electrolyte solution having a temperature T1.

22. The process as claimed in claim 20, further comprising, during a process step, continuously circulating the electrolyte solution present in the reactor by discharging the electrolyte solution from the reactor and replacing the electrolyte solution with the same electrolyte solution.

23. The process as claimed in claim 20, further comprising carrying out the surface coating in a three-stage process in the reactor, with a first process stage being carried out using an electrolyte solution having a temperature T1, a second process step subsequently being carried out using an electrolyte solution having a temperature T2T1, and a third process step being carried out using an electrolyte solution having a temperature T3T2.

24. The process as claimed in claim 23, further comprising carrying out the process so that the temperature T3 is equal to the temperature T1.

25. The process as claimed in claim 20, further comprising applying a layer of a compound, which can be oxidized by an applied electrolyte solution and which has a viscosity of at least 1000 mPas at 25 C., to the body (4) before the electrochemical deposition of the surface coating.

26. The process as claimed in claim 25, further comprising using a polyhydroxy compound as the compound to be applied to the body before the electrochemical application of the surface coating.

27. The process as claimed in claim 26, further comprising selecting the polyhydroxy compound from the group consisting of glycerol, carbohydrates, and polyethylene glycol.

28. The process as claimed in claim 26, further comprising cleaning the body with an alcohol before application of the layer of a polyhydroxy compound.

29. The process as claimed in claim 20, further comprising using a rotationally symmetric body as the body.

30. The process as claimed in claim 29, further comprising rotating the body during the surface coating.

31. The process as claimed in claim 20, further comprising, during the surface coating, using a ventilation system to remove formed gases from the reactor.

32. An apparatus for the electrochemical application of a surface coating, for carrying out a process as claimed in claim 20, comprising a reactor for accommodating a body, to be coated, an anode and at least two electrolyte containers, wherein the electrolyte containers are connected to the interior of the reactor via connecting conduits through separate inlets and outlets.

Description

[0064] The FIGURE shows:

[0065] FIG. 1 a schematic depiction of an apparatus according to the invention for carrying out the process of the invention

EXAMPLE 1

[0066] FIG. 1 is a schematic depiction of an apparatus according to the invention for carrying out the process of the invention. The apparatus 1 comprises a reactor 2 for carrying out the electrochemical process. The reactor 2 is closed by a lid 3 which can be taken off.

[0067] A body 4 to be coated, preferably a rotationally symmetric body, is introduced as cathode into the reactor 2. Furthermore, an anode 5 which preferably consists of platinated titanium is arranged in the reactor 2. The body 4 to be coated is connected via a rotatable rod 6 to the lid 3.

[0068] Electrolyte solution from the electrolyte containers 7, 8 can be introduced via connecting conduits 7a, 8a into the reactor 2. In FIG. 1, only two containers 7, 8 with respective connecting conduits 7a, 8a are shown; however, additional containers and connecting conduits can also be provided if required. The connecting conduits 7a, 8a can be opened and closed by means of shut-off devices 7b, 8b, which are preferably valves, so that only one particular electrolyte goes, in a targeted manner, into the reactor 2.

[0069] The connecting conduits 7a, 8a end in inlets which are arranged in the bottom plate of the reactor 2. Outlets via which electrolyte can flow out and flow back via connecting conduits 7c, 8c into the electrolyte containers 7, 8 are arranged in the upper third of the reactor 2. The connecting conduits 7c, 8c can be opened and closed by means of shut-off devices 7d, 8d, which are preferably valves, so that only one particular electrolyte goes, in a targeted manner, from the reactor 2 into the electrolyte container 7, 8 provided.

[0070] Pumps (not shown) are provided for conveying the electrolyte through the conduits 7a, 7c, 8a, 8c.

[0071] A rectifier 9 operated using an alternating voltage supplies the cathode 4 and anode 5 with the direct current necessary for the process via electric conductors 9a, 9b.

[0072] The apparatus 1 is controlled by means of an electronic process control unit (not shown).

[0073] According to the invention, the rotationally symmetric body is preferably pretreated before it is introduced into the reactor 2. After a mechanical surface treatment, for example by grinding or sandblasting, the surface of the body 4 is firstly cleaned using a cleaning cloth impregnated with ethanol. A film of polyethylene glycol 1500 (from Merck) is subsequently applied to the surface of the body 4 by means of a vibratory grinder.

[0074] The body 4, for example a steel cylinder, which has been pretreated in this way is introduced into the reactor 2 and the reactor 2 is closed by means of the lid 3. A mixture of 250 g of CrO.sub.3 and 2.5 g of sulfuric acid in 1 l of water is then pumped as electrolyte from the container 7 into the reactor 2. The electrolyte is heated to 50 C. beforehand. The body 4 is rotated, electric current is applied and a first chromium layer is formed. During this first process step, the shut-off devices 7b and 7d are opened and the shut-off devices 8b, 8d are closed, and the electrolyte from the container 7 is circulated continuously.

[0075] After the first process step is complete, the shut-off device 7b is closed and the shut-off device 8b is opened instead. The shut-off device 7d remains open, while the shut-off device 8d is closed. A mixture of 250 g of CrO.sub.3 and 2.5 g of sulfuric acid in 1 l of water is then pumped as electrolyte from the container 8 into the reactor 2. The electrolyte is heated to 37 C. beforehand. The electrolyte from the container 8 displaces the hotter electrolyte originating from the container 7 back into the container 7 via the conduit 7c. As soon as the electrolyte from the container 7 has been completely displaced from the reactor 2, the shut-off device 7d is closed and the shut-off device 8d is opened. The electrolyte from the container 8 is now present in the reactor 2. The body 4 is rotated, electric current is applied and a second chromium layer (structured layer) is formed. During this second process step, the shut-off devices 8b and 8d are opened, and the electrolyte from the container 8 is recirculated continuously.

[0076] After the second process step is complete, the shut-off device 8b is closed and the shut-off device 7b is opened instead. The shut-off device 8d remains open, while the shut-off device 7d is closed. A mixture of 250 g of CrO.sub.3 and 2.5 g of sulfuric acid in 1 l of water is then pumped as electrolyte from the container 7 into the reactor 2. The electrolyte is heated to 50 C. beforehand. The electrolyte from the container 7 displaces the hotter electrolyte originating from the container 8 back into the container 8 via the conduit 8c. As soon as the electrolyte from the container 8 has been completely displaced from the reactor 2, the shut-off device 8d is closed and the shut-off device 7d is opened. The electrolyte from the container 7 is then present in the reactor 2. The body 4 is rotated, electric current is applied, and a third chromium layer (covering layer) is formed. During this third process step, the shut-off devices 7b and 7d are opened, and the electrolyte from the container 7 is circulated continuously.

[0077] During all process steps, the gas atmosphere in the reactor 2 can be drawn off by means of a pump (not shown) in order to prevent formation of a hydrogen/oxygen gas mixture.

[0078] After the third process step is complete, the shut-off device 7b is closed, while the shut-off device 7d remains open. The entire electrolyte is removed from the reactor 2. The coated body 4 is cleaned using water or an aqueous solution which is introduced from a conduit (not shown) into the reactor 2. The cleaning water is subsequently discharged from the reactor 2 and purified. The reactor 2 is then opened and the coated body 4 is taken out.